The present invention relates to a method for producing a hot CO- and H.sub.2 -containing reducing gas serving for the reduction of lumpy metal ore, in particular iron ore, wherein the reducing gas is formed in a gasification zone by the gasification of carbon carriers, in particular coal, taking place under a supply of oxygen and subsequently cooled down to a reducing-gas temperature favorable to the reduction process, and a plant for carrying out the method.
A method of the initially described kind is known i.e., from DE-C - 30 34539 and from EP-B 0 114 040. With these known methods, pig iron or a steel pre-product are produced by smelting from at least prereduced sponge iron in a meltdown gasifying zone under the supply of carbon carriers and oxygen-containing gas, and a CO- and H,-containing reducing gas is generated. The reducing gas formed in the meltdown gasifying z one exhibits a temperature in the range of 1000 to 1200.degree. C. At this temperature, the released hydrocarbon compounds are decomposed. At the same time, the CO.sub.2 and H.sub.2 O contents drop to below 6% CO.sub.2 and 4% H.sub.2 O on account of these temperatures, since they are converted to CO and H.sub.2.
For utilization in a reduction reactor, this very hot reducing gas has to be cooled prior to introduction into the reduction reactor. In accordance with DE-C - 30 34 539 fi., a spray cooler with a subsequently connected scrubbing tower is provided to that end. The portion of the reducing gas thus cooled is admixed with the reducing gas exiting the melt-down gasifying zone. Such routinely effected cooling of the reducing gas by cooled reducing gas of the same type to roughly 700 to 900.degree. C prevents the occurrence of incipient melting of the ore particles in the reduction zone during ore reduction, but without causing a decrease in the reduction potential of the reducing gas.
Yet it is disadvantageous that the reducing gas thus cooled is thermodynamically unstable; from the carbon monoxide, carbon dioxide and carbon form in accordance with the Boudouard equilibrium, just as in accordance with the heterogeneous water-gas equilibrium a reaction of carbon monoxide with hydrogen to water and carbon takes place, which reaction is also exothermnic, like the reaction described first. This leads to an increase in temperature of the reducing gas and hence to an increase in temperature of the shaft material. There will tie the formation of agglomerates. Thus not only is the reduction process affected but the yield of shaft material from the reduction zone is affected as well.
The present invention aims at avoiding these disadvantages and difficulties and has as its object to provide a method of the initially described kind and a plant for carrying out the method, enabling a reducing gas to be produced having a temperature range that is favorable to the reduction of the metal ore, hence lying below the temperature at which instances of incipient melting and fouling (formation of agglomerates) may occur in the at least partially reduced metal ore. Moreover, a chemical attack on the metallic materials of the gas-carrying systems, that is, reactors and gas conveying ducts, built-in structures etc., is to be avoided.